To find out how much the car's value decreases per month, you can divide the total decrease in value by the number of months (12 months).
The car's value decreases by $4,000 over 12 months.
\[ \text{Monthly decrease} = \frac{\text{Total decrease}}{\text{Number of months}} = \frac{-4000}{12} \approx -333.33 \]
So the car's value decreases by approximately -333.33 per month.
The answer is A: negative 333.33.